1. Technical Field
The present disclosure relates to methods and devices for measuring electromagnetic signals and, particularly, to a carbon nanotube based method and device for measuring certain properties of an electromagnetic signal.
2. Description of Related Art
Polarizing direction and intensity are two important properties of an electromagnetic signal. A related art method for measuring the polarizing direction of a visible light includes steps of: disposing a polarizer and a target in the path of the visible light, and rotating the polarizer. The polarized visible light goes through the polarizer and irradiates the target. During rotation of the polarizer, the light on the target changes periodically from the dark to the bright. When the light on the target is darkest, the polarizing direction of the visible light is perpendicular to the polarizing direction of the polarizer. When the light on the target is brightest, the polarizing direction of the visible light is parallel to the polarizing direction of the polarizer. Thus, one can tell the polarizing direction of the visible light by observing the light on the target. Similar, one can qualitatively tell the intensity of the visible light by observing the brightness or darkness of the visible light.
However, the above observing methods for determining the intensity and polarizing direction are not suitable for invisible light such as infrared, ultraviolet, and other electromagnetic signals. In general, to measure the intensity and polarizing direction of invisible light, a photoelectric sensor is disposed at the target position. Thus, the invisible light is transformed to electric signals, and the electric signals can be measured.
However, the method for measuring the invisible light is complicated and requires a lot of optical and electrical devices. Besides, the conventional polarizers can only achieve good polarization in a certain regions of the electromagnetic spectra, (e.g. microwave, infrared, visible light, ultraviolet, etc.), but can't have a uniform polarization property over the entire spectrum. Thus, when the wavelength of the light changes, the polarizer has to be changed accordingly.
The photoacoustic effect is a kind of the thermoacoustic effect and a conversion between light and acoustic signals due to absorption and localized thermal excitation. When rapid pulses of light are incident on a sample of matter, the light can be absorbed and the resulting energy will then be radiated as heat. This heat causes detectable sound signals due to pressure variations in the surrounding (i.e., environmental) medium. The photoacoustic effect was first discovered by Alexander Graham Bell (Bell, A. G: “Selenium and the Photophone” in Nature, September 1880).
At present, photoacoustic effect is widely used in the field of material analysis. For example, photoacoustic spectrometers and photoacoustic microscopes based on the photoacoutic effect are widely used in the field of material analysis. A known photoacoustic spectrum device generally includes a light source such as a laser, a sealed sample room, and a signal detector such as a microphone. A sample such as a gas, liquid, or solid is disposed in the sealed sample room. The laser is irradiated on the sample. The sample emits sound signals due to the photoacoustic effect. Generally, different materials have different maximum absorption at different laser frequencies. The microphone detects the frequency of the laser light where the sample has the maximum absorption. However, most of the sound signals are not strong enough to be heard by human ear but detected by complicated sensor, and the frequency of the sound signals can even be in the region above megahertz (MHz).
Carbon nanotubes (CNT) are a novel carbonaceous material having extremely small size and extremely large specific surface area. Carbon nanotubes have received a great deal of interest since the early 1990s, and have interesting and potentially useful electrical and mechanical properties, and have been widely used in a plurality of fields.
What is needed, therefore, is to provide a simpler method and device for measuring intensity and polarizing direction of an electromagnetic signal.
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one embodiment of the present method and device for measuring intensity and polarizing direction of an electromagnetic signal in at least one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.